GB2269206A - Mixing domestic hot and cold water supplies. - Google Patents

Abstract

Apparatus for the mixing of hot and cold water where the cold water is fed from a mains supply comprises a T-connector having a cold water conduit branch (24), a hot water conduit branch (24) and a mixed water conduit branch (28). Mounted concentrically in the branches (22, 28) is a reduced diameter pipe extension (30) through which hot water flows into the conduit (28) for admixture with the cold water also passing into the conduit (28) through the annular space (32) surrounding the extension (30). The dimensions of the conduit (28) and the extension (30) are such that the annular passage (32) causes the mains supplied cold water to flow therethrough with increased velocity so that it enters the conduit (28) at a velocity which is greater than the velocity of gravity fed hot water pumped through the extension (30). In a second embodiment the hot water flows through the annular space and the cold water through the extension, the latter being provided with a restricted outlet. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO WATER SUPPLIES This invention is concerned with improvements in or relating to water supplies and is particularly although not exclusively concerned with apparatus for mixing hot and cold water in domestic shower units.

Domestic shower units are essentially of two common types, namely those in which both hot and cold water are fed under gravity and mixed to flow to the shower head for delivery therefrom, and those in which both supplies of water are pumped to the shower head, but a third type is possible namely that in which only the hot water is pumped, with the cold water being supplied at mains pressure. This latter type has achieved little popularity due to problems of mixing water supplies of unequal pressures.

This invention is particularly concerned with water supplies for the last mentioned type of shower unit, namely that in which there is a substantial difference in pressure between the cold water supply and the hot water supply to the shower unit.

There are two inherent problems with such systems, the first of these being that to equalise the difference in pressure, it is necessary either to reduce the pressure of the cold water supply by restricting the flow of cold water, which is in itself wasteful of energy or it is necessary to pump the hot water from the domestic hot water supply at a pressure such that it matches the pressure from the cold water supply. Suppliers of many currently-available commercial powered shower units (i.e.

those including pumps) seek to achieve the latter due to the customer's apparent desire and the current vogue to provide higher pressure jetted water than was hitherto provided by gravity fed systems.

The second problem with systems that rely on mains cold water pressure is in no small measure the reason for having to deal with the first problem, namely that mains pressure of the cold water supply can cause the flow of cold water through the system to be at such a rate that either there is not uniform mixing of the cold water with the hot water at the interface where the two supplies meet or a pump of sufficient capacity has to be provided to deliver hot water at a substantially higher pressure to ensure mixing. If hot water is supplied from a pump as a gravity feed supply, it is observed that the flow of cold water can prevent hot water from mixing with the cold water.

A consequence of compensating for the differences in pressure is that mixed water is then delivered at a rate which is more than adequate or a restrictor has to be inserted in the system to reduce the mixed water pressure, both alternatives being wasteful of energy.

In addition to the above problems, it is necessary to use powerful pumps in powered shower systems to pressurise gravity based systems and such pumps add significantly to the overall cost of the shower units and to the running costs thereof.

The present invention seeks to provide a solution to the above problems by providing apparatus for use in shower units which will, in a simple manner, provide for more efficient mixing of hot and cold water in a differential pressure system and will, at the same time, allow for a lower powered pump to be used than hitherto in such systems.

The present invention provides, in or for a domestic hot water system, apparatus for mixing cold water fed from a mains supply with hot water fed from a gravity fed hot water supply, the apparatus comprising a cold water conduit and mounted concentrically therein an extension or fitting through which hot water can flow into the conduit for admixture with the cold water, the dimensions of the cross-sections of the conduit and the fitting being such as to provide an annular passage therebetween through which mains supplied cold water can flow for admixture with gravity fed hot water.

In a modification (not shown) of the aforementioned apparatus, the extension or fitting may be provided with external vanes which are formed so as to guide the cold water flow to impart a component of circular motion to the otherwise linear flow through the annular passageway.

In yet another embodiment of the apparatus, the extension or fitting may be replaced by an extension which has a thicker wall than the extension or fitting referred to above and which fits tightly in the outlet pipe, the extension or fitting being provided with a plurality of longitudinal slots or grooves which are connected by an annular groove adjacent the cold water inlet, and the slots or grooves being closely spaced around the periphery of the exterior of the extension or fitting.

As a further alternative, the slots or grooves may be formed so as to impart a component of circular motion to the cold water before it mixes with the hot water. In either case the outlet ends of the slots or grooves may be flared.

The present invention also provides, in or for a domestic hot water system, apparatus for mixing cold water fed from a mains supply with hot water fed from a gravity fed hot water supply, the apparatus comprising a hot water conduit and mounted substantially concentrically therein an extension or fitting through which cold water can flow to be admixed in the conduit with the hot water, the extension or fitting providing a restricted orifice through which cold water is forced by mains pressure to be admixed with hot water.

By adopting the proposed invention, two effects are achieved, namely that the inherent resistance to flow of the pumped water in the conduit piping (an effect known in water technology as stiction) is reduced because the effect of the injection of the cold water into the flow of hot water is to reduce the amount of stiction between the flowing hot water and the interior of the conduit and so increase the flow rate of the hot water as it mixes with the cold water from the pump; this will then reduce the pressure of the hot water flowing from the pump and thus the load on the pump. Effectively, the reduced load on the pump results in the pump being able to deliver a greater rate of flow and thus allows a lower powered pump to be employed than hitherto.

In addition, it is possible to ensure that hot and cold water will be properly admixed as the combined flow advances towards the shower head.

The principle upon which the invention is founded is to utilise the energy of the mains cold water supply to enhance the combined water flow.

There now follows a description which is to be read with reference to the accompanying drawings of to forms of apparatus according to the present invention; it is to be clearly understood that these two forms of the invention have been selected for description to illustrate the invention by way of example and not by way of limitation.

In the accompanying drawings: Figure 1 is a diagrammatic illustration of the principles upon which the first form of apparatus according to the invention is based; Figure 1A is a sectional view of a first form of apparatus according to the invention; Figure 2 is a diagrammatic illustration of the principles upon which the second form of apparatus according to the invention is based; and Figure 2A is a sectional view of a second form of apparatus according to the invention.

Referring firstly to Figure 1, there is shown therein in schematic form, a conduit 10 which in the present case, is a cold water conduit through which mains supplied cold water can flow. Mounted concentrically within the conduit 10 is a second conduit 12 through which gravity fed hot water can flow into the conduit 10 for admixture with the cold water.

If the hot water is permitted to flow through the conduit 12 while the supply of cold water is shut off, the velocity distribution curve 14 of the hot water flow across the conduit 12 is substantially as shown in Figure 1. This is due to an effect which is currently referred to as 'stiction' and means the combined effect of the viscosity of the water and the friction of the interior walls of the conduit providing a drag effect on the water flow adjacent the walls to produce the velocity curve.

In narrow 15mm domestic conduit, the effect of stiction can provide a considerable resistance to flow in the conduit. It is therefore desirable to reduce this effect as much as possible because, with a pumped hot water system, the effect also affects the ability of the pump to deliver water through the conduit and so reduces its maximum output.

It is foreseen by the present invention that this adverse effect can be reduced in practice by deliberately increasing the velocity of the water flow at and adjacent the surface of the interior walls of the conduit and it is this that the present invention seeks to achieve.

To increase the velocity of the water requires the supply of energy; such energy is available from the mains supplied cold water, the supply of which is at greater pressure than the hot water supply. By using the available energy and directing this through the annular cold water flow that is fed by the first apparatus according to the invention into the hot water flow, the flow rate of the mixed water can be increased and the back pressure on the pump delivering hot water can be reduced considerably. An illustrative example of the effect of the annular cold water flow is shown in the velocity distribution curve 16 shown in Figure 1.

Stiction still has an effect on the annular cold water flow but the greater velocity of the cold water flow reduces its effect.

The net effect of the system shown in Figure 1 is to reduce the load on the hot water pump and allow it to deliver an increased rate of flow of hot water.

In Figure 1A, there is shown a practical example of apparatus according to the invention in which a Tconnector 20 provides the junction between the hot and cold water supplies, the hot water supply being delivered from a pump through a pipe 22 and mains supplied cold water being delivered through a pipe 24; both pipes are standard 15mm external diameter pipes.

The T-connector may be of the type which is illustrated in Figure 5 of the drawings accompanying European patent no. 334648 and is manufactured by John Guest Engineering Limited of West Drayton, Middlesex, England. Such a connector comprises a connector body 21 believed to be made from polysulphone polymer material and having collar members 23 which are mounted in each of the three outlets of the connector body to allow a push fit of a standard bore water pipe into the connector to allow it to be coupled therewith and only to be released by holding the collar member against the connector body as the pipe is withdrawn. This type of connector is suitable for use with standard bore pipe lengths made of plastics material, principally polypropylene material, and provides advantage over the traditional copper pipe installation because it does not require solder.

In normal domestic water mixing shower arrangements, the water being delivered through the two pipes 22 and 24 would begin to mix to the extent possible inside the cavity 26 of the T-connector 20 and would continue to mix as the water exits the T-connector through an outlet pipe 28.

According to the present invention, the hot water inlet pipe is provided with an extension 30 which may be integrally formed with the pipe 22 or it may be provided as a separate piece which can either be tightly fitted into the end of the pipe 22 or can be bonded into the pipe 22. The extension 30 is of reduced diameter, e.g.

10mm, has an internal diameter of approximately 5mm and is of sufficient length that, when the pipe 22 is inserted into the T-connector 20, the extension 30 extends across the internal cavity 26 of the T-connector 20 into the outlet pipe 28, the external diameter of the extension 30 being such that an annular passageway 32 is defined between the outer surface of the extension and the inner surface of the outlet pipe 28. The width of the annulus is approximately lmm.

Effectively, this arrangement causes the mixing of hot water with cold water in the outlet pipe 28 and not in the cavity 26. Hot water flows through the pipe 22 and the extension 30 into the outlet pipe 28 and there it is mixed with cold water forced through the annular passageway 32. Under mains pressure, the cold water forced through the restriction provided by the annular passageway 32 increases velocity as it passes through the passageway and enters the outlet pipe 28 as an annular flow of water which is flowing faster than the pumped supply of hot water. The net effect is to increase the velocity of the total flow of water through the outlet pipe 28. This in turn decreases the load on the pump supplying the hot water and allows the pump to increase the flow of water that it can deliver.

With pumps of the type normally used in powered shower units, this increase in efficiency of the pump means that the pump is then capable of providing a rate of flow of hot water which is greater than is needed for a shower unit. In consequence it is possible to employ pumps of smaller capacity than hitherto with consequent cost saving.

In tests carried out by the applicants, it has been found that the flow rate of hot water, when the hot water passes through the extension 30 and is admixed with cold water flowing through the annular passageway, increases by approximately 36% as compared with the flow rate when known mixing systems are used.

In a modification (not shown) of the apparatus shown in Figure lA, the extension 30 may be provided with external vanes which are formed so as to guide the cold water flow to impart a component of circular motion to the otherwise linear flow through the annular passageway.

In yet another embodiment (not shown) of the apparatus shown in Figures lA, the extension 30 may be replaced by an extension which has a thicker wall than the extension used in the apparatus of Figures 1A and 1B and which fits tightly in the outlet pipe 28, the extension being provided with a plurality of longitudinal slots or grooves which are connected by an annular groove adjacent the cold water inlet, and the slots or grooves being closely spaced around the periphery of the exterior of the extension. As a further alternative, the slots or grooves may be formed so as to impart a component of circular motion to the cold water before it mixes with the hot water. In either case the outlet ends of the slots or grooves may be flared.

Referring now to Figure 2, there is shown therein in schematic form, a conduit 40 which is a hot water conduit through which gravity fed hot water can be supplied from a pump (not shown). Mounted concentrically, or at least substantially so, within the conduit 40 is a second conduit 42 through which mains supplied cold water can flow into the conduit 40 for admixture with the hot water.

The hot water flows through the annulus defined between the two conduits 40 and 42, the rate of flow being dependent upon the pressure imparted to the flow by the pump and any gravitational force acting on the water. In general, such combined force as is exerted on the water is considerably less than the pressure at which the cold water is supplied from a mains supply, and the present invention foresees that this difference in water supply pressure can be utilised to improve both the mixing and flow rate of mixed water in a domestic powered shower unit.

As has been outlined above with reference to the previous embodiment, water, in this case hot water, flowing from a pump to a shower head is subject to stiction which acts to resist the flow. This has an effect on the rate at which a pump can deliver water and thus determines the capacity of pump that must be used in a domestic shower unit, having regard to pipe dimensions and the like.

The second embodiment of the invention again utilises the greater pressure of the mains cold water supply to overcome this problem by restricting the outlet 44 of the cold water conduit 42 so that the cold water issues as a jet from the outlet with considerably greater force to mix with the hot water and increase the velocity of the flow of mixed water through the conduit 40, and thus reduce the load on the hot water pump.

In Figure 2A, there is shown a practical example of apparatus according to the invention in which a Tconnector 50 provides the junction between the hot and cold water supplies. In this case, and to demonstrate the versatility of the invention and how it may be used to adapt existing domestic shower systems, the Tconnector that is illustrated is one which provides a coupling 52 for a 25mm external diameter pipe and two couplings 54 and 56 for 15mm pipes, one of which 54 is coaxial with the 25mm coupling. The hot water supply is delivered from a pump through a 15mm pipe 58 and mains supplied cold water is delivered through a 15mm pipe 60; in this case, the cold water inlet pipe is coupled to the 25mm coupling 52 of the T-connector.The end of the cold water pipe is mounted in a cylindrical 25mm external diameter adaptor fitting 62 which fits in watertight manner in the coupling 52 and which provides a reducing connector for connecting the 15mm pipe to a 10mm pipe 66 formed of suitable plastics material and having a wall thickness from 1.5mm to 2mm. (Alternatively, the fitting could provide a reducing connector for connecting a 25mm pipe to a 10mm pipe). The connector has an axial aperture 64 therein through which the length of 10mm pipe 66 can extend in watertight engagement with the fitting 62, the pipe 66 extending through the cavity 68 of the Tconnector 50 and into an outlet pipe 70 where the pipe 66 lies substantially coaxially with the outlet pipe.The outlet 69 of the pipe 66 is of restricted diameter, typically 3mm, the restriction being provided either by forming the pipe or by inserting an annular restrictor into the end of the pipe.

The pipe 66 and the pipe 70 define an annulus therebetween of width approximately lmm and through which hot water delivered through the inlet pipe 58 can flow from the pump and under gravity to a shower head. Below the end of the pipe 66 the hot water mixes with the cold water, the latter being at greater pressure than the hot water and flowing through the restricted outlet 69 with even greater velocity than in the pipe itself, with the net effect that the flow rate and the pressure of the cold water increases that of the hot water and thus of the total flow of water through the pipe, thereby to provide the same advantages as with the first embodiment described above.

In tests that the applicants have carried out, it has been found that, using apparatus according to the invention, it has been possible to achieve a combined hot-and cold flow rate which is 175% of the original flow rate where the apparatus was not so used but known systems of water mixing were employed.

Claims (7)

1 In or for a domestic hot water system, apparatus for mixing cold water fed from a mains supply with hot water fed from a gravity fed hot water supply, the apparatus comprising a cold water conduit and mounted concentrically therein a fitting through which hot water can be pumped into the conduit for admixture with the cold water, the dimensions of the cross-sections of the conduit and the fitting being such as to provide an annular passage therebetween through which mains supplied cold water can flow for admixture with the hot water.

2 Apparatus according to claim 1 wherein the fitting is provided with external vanes which are formed so as to guide the cold water flow to impart a component of circular motion to the otherwise linear flow through the annular passageway.

3 Apparatus according to claim 1 wherein the fitting is replaced by an extension which has a thicker wall than the fitting and which fits tightly in the outlet pipe, the fitting being provided with a plurality of longitudinal slots or grooves which are connected by an annular groove adjacent the cold water inlet, and the slots or grooves being closely spaced around the periphery of the exterior of the fitting.

4 Apparatus according to claim 3 wherein the slots or grooves are formed so as to impart a component of circular motion to the cold water before it mixes with the hot water.

5 Apparatus according to either one of claims 3 and 4 wherein the outlet ends of the slots or grooves may be flared.

6 In or for a domestic hot water system, apparatus for mixing cold water fed from a mains supply with hot water pumped from a gravity fed hot water supply, the apparatus comprising a hot water conduit and mounted substantially concentrically therein a fitting through which cold water can flow to be admixed in the conduit with the hot water, the fitting providing a restricted orifice through which cold water is forced by mains pressure to be admixed with hot water.

7 In or for a domestic hot water system, apparatus substantially as hereinbefore described with reference to the accompanying drawings.